Help! Computer shutting off?

[nikolai]

Just recently rebuilt my computer. Most everything in this system is brand new.

Here's my build:

Antec 900 case
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129021

2x 2gb RAM
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231122

500w Power Supply
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371007

Motherboard:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128364

Quad-Core 2.4 GHz Processcor (Though BIOS is saying it's running at 1.66 right now):
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115017

Hard Drive:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136319

Can't remember what my vid card is off the top of my head, but it's a Sapphire Radeon, and an old model which worked perfectly with my old build. It's the only thing I haven't replaced.

The problem is that my computer will start up, most of the time it will even POST. It's managed (once) to get all the way to formating the hard drive to install my operating system (Brand new hard drive, so it's got nothing on it) but it dies. Sometimes it'll turn on for a second and die. Everything seems to be connected properly, everything seems to be turning on. All fans are running. It seemingly random when it decides to stay on and when it doesn't. I'm at a loss as to what the problem could be at this point =/

 

[netxuser]

maybe your computer is grounded, please check if you tighten all the screws, remove the memory and put it again, and also check if there is a latest update for your bios.

 

[nikolai]

Screws are tight, BIOS is reading the memory (But I will try removing it and putting it back in anyway) and it seems as though I have the latest. The newest release is a beta, not sure if I want to flash the bios on that 'un. This is the first time I've built a system, so I'm not sure I'd even do it right.

 

[nikolai]

I replaced the 500w with

http://www.newegg.com/Product/Product.aspx?Item=N82E16817152033

Thinking it was a PSU problem. And it's still shutting down. I'm at a loss of what to do.